In conventional warehouse transporting systems, a shelving and unshelving and transporting electric car travels on rails installed along a car passage between adjacent racks. Generally in the driving system employed in the known transporting systems, an electric motor drives the traction wheels of the transporting electric car. The power supply for the electric car includes an electric line extending along the car passage and a collector on the car in a sliding contact with the line.
In such conventional transporting systems, the traction wheel drive and the power supply system had numerous problems. For example, the electric car makes considerable noise when it moves, even though it cannot run fast. Due to the dust produced by such supply systems and other obstacles, there is often a failure of smooth and constant supply of electric current to the car.
The noise of the car can be reduced and its speed can be increased by employing a linear motor body mounted on and attached to the car and cooperating with a secondary conductor secured along the passage. The motor body must be separated at all times by a predetermined small clearance from the secondary conductor. Abrasion of the outer periphery of the wheels and/or any obstacle intervening between any running wheel and the running surface of the passage will result in a variation in the effective height of the electric car and particularly of the linear motor body whereby the required clearance cannot be maintained or in a worst case the linear motor body could even directly contact the secondary conductor.
The aforementioned drawbacks of the prior art systems can also be resolved in another way. An induction wire line (such as a wire known as the "litz" wire) can be installed in an along each car passage, as a noncontact type power source, with at least one induction coil being carried by the car. When many car passages are used, one above another, in a multi-level automated warehouse, each car passage requires a panel for power supply, thereby noticeably raising construction costs.